This invention relates to a method for determining the components of image noise patterns of an imaging device and use of this method in an imaging device. More particularly, this invention relates to a method for the separation of the components of nonuniformity assignable to banding (one-dimensional periodic noise), streaking (one-dimensional random noise), and granularity (two-dimensional random noise) from a flat field scan produced by a digital imaging system.
Certain photographic or digital imaging components introduce a two-dimensional random noise into the image. In photographic components, this is the result of the random distribution of the photographic imaging elements or grains, and is termed granularity. In digital components, such two-dimensional noise can be generated by quantum or thermal fluctuations which are introduced into the electronic signal recorded by the individual pixels, and which vary randomly from pixel to pixel. Furthermore, digital imaging components may also introduce one-dimensional artifacts into the image, such as banding (one-dimensional periodic noise) or streaking (one-dimensional random noise). The spatial structure of these artifacts can be characterized by examining their microdensity profile, which can be thought of as a plot of the opacity of the image as a function of x and y spatial coordinates. The banding artifact is characterized by regularly spaced lines having a periodic microdensity profile, whereas the streaking artifact is characterized by a superposition of lines of random width, and spacing, leading to a random microdensity profile. Banding may result from periodic positioning errors in the placement of a one-dimensional pixel array, whereas streaking may result from random variations between the responses of adjacent pixels in a one-dimensional array. In all cases, the above artifacts are most visible and objectionable in uniform or featureless areas of an image.
During the development and manufacture of imaging components, such components are frequently tested for their tendency to introduce the above artifacts by examination of a flat field or featureless image produced by the imaging system. For example, such an image can be produced by capturing a uniform gray or colored background in a camera or scanner, and examining the captured image. In another example, a digital printer can be tested by creating a synthetic digital image in which all pixels are set to exactly the same digital code value, printing or displaying this image, and examining the output.
Several techniques have been suggested in the technical and patent literature for the evaluation and correction of the above artifacts in image or signal data. Most of these techniques pertain directly to the correction of the images or output produced by the system. For example, U. S. Pat. No. 4,956,873 issued Sep. 11, 1990 to Hockley et al., entitled xe2x80x9cImage Processing Apparatusxe2x80x9d discloses an image processing apparatus for the correction of banding, while others have described image processing algorithms which attempt to filter out the banding from the resulting digital image (see S. Hummer-Miller, xe2x80x9cTechniques for Noise Removal and Registration of TIMS Dataxe2x80x9d, Photogrammetric Engineering and Remote Sensing, Vol. 56, No. 1, January 1990, pages 49-53; or D. L. Helder,et al., xe2x80x9cA Technique for the Reduction of Banding in Landsat Thematic Mapper Imagesxe2x80x9d, Photogrammetric Engineering and Remote Sensing, Vol. 58, No. 10, October 1992, pages 1425-1431). The removal of random lines from the image background has also been addressed (see J. Beyerer et al., xe2x80x9cAdaptive Separation of Random Lines and Backgroundxe2x80x9d, Optical Engineering, Vol. 37, No. 10, October 1998, pages 2733-2741). Other examples have addressed the issues of signal recovery in the presence of artifacts, via spectral analysis (see U. S. Pat. No. 5,892,700 issued Apr. 6, 1999 to Martin Haardt, entitled xe2x80x9cMethod for the High-Resolution Evaluation of signals for One or Two-Dimensional Directional or Frequency Estimationxe2x80x9d), or texture analysis and segmentation (see R. Navarro et al., xe2x80x9cRobust Method for Texture Synthesis-by-Analysis Based on a Multiscale Gabor Scheme,xe2x80x9d Proceedings of the SPIE, Vol. 2657, pages 86-96, 1996; or D. Carevic et al., xe2x80x9cApplication of Partial Modeling Techniques for Texture Segmentation,xe2x80x9d Journal of the Optical Society of America, Vol. 14, No. 11, November 1997, pages 2924-2937). In U.S. Pat. No. 5,537,669 issued Jul. 16, 1996 to Braddon et. al. entitled xe2x80x9cInspection Method and Apparatus for the Inspection of Either Random or Repeating Patternsxe2x80x9d, the semiconductor industry has developed techniques for defect inspection which rely on the identification of repeating patterns.
In the characterization of imaging component performance at the design or manufacturing stages, it is crucial to obtain precise and accurate data pertaining to the artifacts introduced by these components. The most accurate data will be derived from flat field scans, in which the artifacts are most visible and can be most accurately characterized, given the absence of image features. More importantly, the task of characterizing and separating the artifacts described above is considerably more complex when the artifacts are present in combination. One, two or all three of the artifacts may be present in practical devices. None of the aforementioned techniques addresses this problem.
A goal in the design and manufacture of imaging components, systems, or subsystems is to produce an image free of distortions or artifacts. In particular, it is desirable to prevent or reduce the addition of visible artifacts to the image by the imaging system components.
It is an object of the present invention to provide a method for determining at least one component of a noise pattern of an imaging device, so that this noise pattern component can be characterized, and the device adjusted, thereby producing images free of distortions or artifacts, or images containing reduced distortions or artifacts.
The above object is accomplished by an inventive method for determining at least one component of a noise pattern of an imaging device, comprising the steps of:
providing flat field data with respect to the specific imaging device
forming a preliminary estimate of banding components and streaking components, and
determining the banding components, the two-dimensional random noise statistics and the streaking components.
Another object of the present invention is to provide a computer to program for determining at least one component of a noise pattern of an imaging device and thereby producing images free of distortions or artifacts.
The above object is accomplished by an inventive computer program, embodied on a computer readable medium for determining at least one component of a noise pattern of an imaging device, comprising:
a data input segment providing flat field data with respect to the specific imaging device,
a calculation segment for forming a preliminary estimate of banding components and streaking components which are pat of said flat field data, and
a plurality of data output segments providing a determination of the banding components, a two-dimensional random noise statistics and the streaking components.
A further object of the present invention is to provide an imaging device for determining at least one component of a noise pattern and thereby providing a correction tool for producing images with said imaging device, which are free of distortions or artifacts.
The above object is accomplished by an inventive imaging device, comprising:
a data input segment for providing flat field data,
a control section for forming a preliminary estimate of banding components and streaking components, and determining the banding components,
the two-dimensional random noise statistics and the streaking components, and
a correction section for applying the determined banding components, the two-dimensional random noise statistics and the streaking components to image data.